With the general increase in life expectancy recorded in recent times, especially in developed countries, the prevalence of certain neurodegenerative diseases has been observed. Alzheimer's disease (AD), first characterized in 1906 by the german neuropathologist Alois Alzheimer, is currently the most common one. It is a primarily age-related disease and the most common cause of dementia in older people. Dementia is characterized by progressive loss of memory and cognitive functions, among other diagnostic criteria, being most of them present in the Diagnostic and Statistical Manual of Mental Disorders and described on the National Institute of Neurological and Communicative Disorders Association.
The disease has two general classifications: 1) late onset, which occurs with the highest incidence at about 60 years of age, and 2) early onset, occurring around 40 years. In the US and Great Britain, it represents about 50% of cases of dementia, being estimated that it is the fourth leading cause of deaths of elderly in these countries. Regarding the neuropathological aspect, patients show diffuse cortical atrophy, presence of senile plaques and neurofibrillary tangles, neurovascular degeneration and neuronal loss.
These senile plaques are characterized mainly by the presence of fibrillar deposits of β-amyloid peptide (Aβ), consisting of approx. 40 amino-acid residues. It has been observed high concentration of physiological metal ions such as Zn2+ and Cu2+, in these plaques, which is considered indicative that the interaction of Aβ with these biometais is at the heart of events that lead to aggregation and toxicity of this peptide. The ferric ions, in turn, have also been related to the aggregation of neurofibrillary tangles, in addition to contributing to the oxidative processes that occur in the nerve cells of the body. Something similar occurs in Parkinson's disease with the protein α-synuclein.
The already approved drugs for the treatment of AD are intended to combat deficits associated with reduced cerebral function and fall into two classes: acetylcholinesterase inhibitors and inhibitors of NMDA (N-Methyl-D-Aspartate) receptors. Such drugs seem to act in enhancing the remain of the cognitive function, however, are not able to prevent the progression of the disease, being, therefore, important the development of new therapeutic agents that hold the advance of neurodegeneration as well as, as far as possible, promote their regression. In this sense, an interesting approach is to obtain compounds that inhibit, specifically, abnormal metal-protein interactions. This class of drugs is known as MPACs (metal-protein attenuating compounds) and relate to the allocation and distribution normalization of physiological metal ions.
A classic example is the clioquinol (CQ or PBT1), a substance belonging to the group of 8-hydroxyquinolines, which, however, was abandoned due to certain unwanted side effects, such as subacute myelo-optic neuropathy.
